Heart failure is usually a chronic, long term condition, but may occur suddenly. It may affect the left heart, the right heart, or both sides of the heart. Heart failure may be considered as a cumulative consequence of all injuries and/or stress to the heart over a person's life and the prevalence of heart failure increases constantly. For example, it is estimated that nearly 5 million people in the USA suffer from heart failure and about 400.000 new cases are diagnosed every year. The prevalence of heart failure approximately doubles with each decade of life. Thus, HF has a huge impact on both health economy and the well-being of the people in western society.
Cardiac resynchronization therapy (CRT) is an established method to treat HF in patients with low ejection fraction and widened QRS-complex. The optimal method to monitor the effects of CRT is however under debate. Several sensor techniques have been developed for providing input cardiac data for use in optimizing CRT but so far the medical community has not fully accepted any of the proposed techniques. Most attempts of proving the clinical benefits of CRT optimization have failed. There are some results supporting AVD-optimization (atrioventricular delay) but in fact really no study has shown significant impact of VV-optimization (inter-ventricular delay). There are many conceivable reasons for the lack of results, as briefly touched upon earlier, one reason might be that none of the sensors available can fully replace the qualified judgment of a skilled physician with both sensor output and routine as tools in evaluating a patient's response to CRT—since many of the presented concepts focus solely on the systole. However, there is reason to believe that a more holistic view on the hemodynamics is required to provide reliable optimization of the CRT both for current responders and potentially also for patients that are so called non-responders.
Left atrial pressure (LAP) is a signal that divulges interesting information about the hemodynamics of the patient. In fact, the LAP signal, or the mean of the LAP signal is by many regarded as a reliable measure for use in diagnosis of congestive heart failure and is also successfully used to e.g. titrate drugs (such as diuretics) for heart failure (HF) patients. Clearly, the primary focus and use of LAP has been the study and use of LAP mean, i.e. the average value of the LAP signal over a number of heart cycles.
In U.S. Published Application No. 2006/0224204, methods and systems for adjusting parameters of an implantable medical device in response to a left atrial pressure signal is shown. The LAP signals are analyzed to identify certain characteristics, attributes and/or signal morphologies that correlate to cardiac performance of the patient, which in turn can be used for the adjustment of the operating parameters. Timing relationships of LAP signal attributes and in particular various timing intervals between the v-wave, a-wave and c-wave characteristics can be used for AV delay adjustment. Specifically, the slope of the LAP signal between the a-wave peak and the c-wave peak, the slope of the LAP signal between the c-wave peak and the x-wave valley, and/or the slope of the LAP signal between the x-wave valley and the v-wave peak can be used for optimizing AV delay and other device parameters. The slope of a specific segment of the LAP signal can be maximized in order to optimize the AV delay.
However, there is a need within the art for improved and alternative methods and system that utilized the valuable information content of the LAP signal for optimizing CRT settings such as AV and/or VV delays.